Stupid Question maybe?

You can safely say that is a
Class C /sized/ network.

This is a favorite interview type question of mine, but I won't disqualify a candidate if they can't come up with the reason. It's more of a probe for historical domain knowledge (one of many I'll slip in).

You can safely say that is a
Class C/sized/ network.
But most don't say that. They just say it's
a Class C, which it most assuredly is not.
I heckle them until they can give the correct
answer: leading bits are 110 or it's not a
Class C subnet.

I am certain that I read the RFC years ago, but I can’t remember it. Which RFC?

RFC796 defines the address formats for classes A, B, and C. A starts with a 0 bit, B starts with 10, and C starts with 110 according to said RFC.

It’s an interesting flag at interview for me, if it comes up, but I wouldn’t normally talk about it unless the candidate does first.

-If they don’t know or mention classful networking at all, they’re new (relatively, I’m old), and that’s fine.

-If they can get it right, they’re either a long-timer or have done some network history.

-If they try to use it, and get it wrong, or can’t properly explain it, there’s a warning that they’ve been cramming network skills from some old and/or low-quality sources. I’d start probing for other warning signs like /24s on point-to-point serial links, RIPv1, and the like.